1. Master Swimming Pool Chemical Reference Chart
This master cheat sheet outlines the optimal target ranges recommended by the Association of Pool & Spa Professionals (APSP) and the National Swimming Pool Foundation (NSPF):
| Chemical Parameter | Ideal Range | Acceptable Min/Max | Testing Frequency |
|---|---|---|---|
| Free Available Chlorine (FC) | 2.0 – 4.0 ppm | 1.0 – 5.0 ppm (Salt: 3–5 ppm) | 2 to 3 times weekly |
| Combined Chlorine (CC) | 0.0 ppm | Max 0.2 ppm (Shock at >0.5) | Weekly |
| Acidity / pH | 7.4 – 7.6 | 7.2 – 7.8 | 2 to 3 times weekly |
| Total Alkalinity (TA) | 80 – 120 ppm | 60 – 150 ppm | Weekly |
| Calcium Hardness (Plaster) | 250 – 400 ppm | 200 – 500 ppm | Monthly |
| Calcium Hardness (Vinyl/Fiberglass) | 175 – 250 ppm | 150 – 350 ppm | Monthly |
| Cyanuric Acid / Stabilizer (CYA) | 30 – 50 ppm | Salt pools: 60–80 ppm | Monthly |
| Salinity (Saltwater Pools) | 3,000 – 3,500 ppm | 2,700 – 4,000 ppm | Monthly |
| Borates (Optional Enhancer) | 30 – 50 ppm | 30 – 60 ppm | Twice per season |
2. Free Chlorine vs Combined Chlorine
When testing chlorine, you must understand three critical distinctions:
- Free Available Chlorine (FC): Unbound, active hypochlorous acid ready to sanitize pathogens and oxidize algae.
- Combined Chlorine (CC / Chloramines): Chlorine that has bonded with ammonia, perspiration, cosmetics, or urine. Chloramines cause strong bleach smells and stinging eyes. When CC exceeds 0.5 ppm, superchlorination (shocking) is required to break these chemical bonds.
- Total Chlorine (TC): The sum of both:
TC = FC + CC.
3. The pH & Total Alkalinity Relationship
Total Alkalinity acts as an alkaline buffer that prevents sudden, violent swings in pH (known as pH bounce):
Rule of Thumb: Always test and balance Total Alkalinity before attempting fine adjustments to pH. If TA is below 80 ppm, adding even modest amounts of acid can cause pH to crater, etching plaster and corroding heater heat exchangers.
- To Raise Alkalinity: Add Sodium Bicarbonate (Baking Soda) via our Alkalinity Calculator.
- To Lower Alkalinity & pH: Add Muriatic Acid (31.45% Hydrochloric Acid) or Sodium Bisulfate via our Pool pH Calculator.
4. Calcium Hardness Requirements by Pool Finish
Water has an innate chemical appetite for calcium. If water lacks sufficient dissolved calcium, it will aggressively leach calcium minerals directly from pool plaster, marcite, grout, and pebble finishes, causing pitting, rough etching, and premature shell degradation.
Plaster & Pebble (Gunite)
Target: 250 – 400 ppm. Never allow to drop below 200 ppm. Check dose via our Calcium Hardness Calculator.
Vinyl Liner & Fiberglass
Target: 175 – 250 ppm. Vinyl and gelcoat surfaces cannot be leached, but minimum calcium is necessary to prevent metal heater corrosion and foaming.
5. Cyanuric Acid (Stabilizer) to Chlorine Ratio
Free chlorine must always scale in proportion to cyanuric acid. A fixed 2.0 ppm FC level is insufficient if CYA is 80 ppm. Keep Free Chlorine at a minimum of 7.5% of CYA at all times to prevent algae outbreaks:
| Stabilizer (CYA) | Minimum Free Chlorine | Target Free Chlorine | Shock Free Chlorine (SLAM) |
|---|---|---|---|
| 30 ppm | 2.0 ppm | 3 – 5 ppm | 12 ppm |
| 50 ppm | 4.0 ppm | 5 – 7 ppm | 20 ppm |
| 70 ppm (Salt Pool) | 5.0 ppm | 6 – 8 ppm | 28 ppm |
6. Saltwater Levels & Borate Enhancers
For saltwater pools, chlorinator cells require 3,000 to 3,500 ppm sodium chloride to electrolyze hypochlorous acid efficiently without low-salt error codes. Use our Saltwater Calculator to dose 99.8% pure food-grade pool salt.
Adding 30 to 50 ppm Borates provides a dual benefit: it acts as a secondary buffer against pH drift (especially valuable in aeration-prone saltwater pools) and provides an algaestatic barrier while making water feel noticeably silky on skin.
7. The Langelier Saturation Index (LSI)
LSI measures water balance equilibrium: whether water is corrosive (etching plaster and rusting metal) or scale-forming (depositing crusty calcium carbonate scale on tiles and heaters). An LSI score between -0.3 and +0.3 represents ideal chemical balance.
8. The Ideal Weekly Testing Schedule
- Tuesdays & Fridays: Test Free Chlorine and pH (adjust immediately if out of range).
- Sundays: Test Total Alkalinity and Combined Chlorine.
- First of Every Month: Comprehensive test for Calcium Hardness, Cyanuric Acid, and Salinity.
Chemical Dosage Calculators
Calculate exact ounces and pounds for your pool:
- Master Pool Chemical Calculator - All-in-one dosage calculator.
- Calcium Hardness Calculator - Protect plaster & heaters.
- Pool pH Calculator - Acid & soda ash dosing.
- Pool Alkalinity Calculator - Sodium bicarbonate dosing.
- Saltwater Pool Calculator - Salt bag dosing requirements.